Chiral symmetry in non-Hermitian systems: product rule and Clifford algebra

Abstract: Chiral symmetry provides the symmetry protection for a large class of topological edge states. It exists in non-Hermitian systems as well, and the same anti-commutation relation between the Hamiltonian and a linear chiral operator, i.e., ${H,\Pi}=0$, now warrants a symmetric spectrum about the origin of the complex energy plane. Here we show two general approaches to identify and generate chiral symmetry in non-Hermitian systems, with an emphasis on lattices with detuned on-site potentials that can vary in both their real and imaginary parts. One approach utilizes the Clifford algebra satisfied by the Dirac matrices, while the other relies on the simultaneous satisfaction of non-Hermitian particle-hole symmetry and bosonic anti-linear symmetry, extended beyond simple spatial transformations to include, for example, an imaginary gauge transformation.